Charging cavities

ABSTRACT

A cavity is charged with particulate material by positioning a predetermined quantity of the material in a box (140). The box has substantially the same horizontal cross-sectional shape as the cavity and is closed at the bottom by at least one door (78) on which the material rests. In order to level the material, the box (140) is moved to and fro horizontally a plurality of times with the energy imparted to the material being progressively reduced during the movements. The door (78) is then opened sufficiently rapidly that the particulate material falls out of the box (140) into the cavity substantially as a unit.

This invention is concerned with charging cavities with particulatematerial.

In various industries, the requirement exists to charge cavities withparticulate material which ideally fills the cavity to a constant depth.The provision of such a level pile is not easy to achieve becauseparticulate material naturally forms an uneven pile if poured into acavity. This can be alleviated to some extent by complex pouringtechniques but this is slow and may be impractical if the cavity is in aconfined space, e.g. between the platens of a press. The possibilityalso exists of over-filling the cavity and skimming off the excessmaterial. This possibility is, however, wasteful of material and may notbe possible in a confined space. This solution is also not availablewhere successive layers of particulate material are deposited on top ofone another. Where there is more than one type of particle in a charge,it is also difficult to maintain uniformity of distribution duringcharging with present charging techniques.

It is an object of the present invention to provide an improved methodof charging a cavity with a particulate material.

The invention provides a method of charging a cavity with particulatematerial, the method comprising positioning a predetermined quantity ofparticulate material in a box which has substantially the samehorizontal cross-sectional shape as the cavity, the box being closed atthe bottom by at least one door on which the particulate material rests,moving the box to and fro horizontally a plurality of times withmovements arranged so that the energy imparted to the material as aresult of the movements is progressively reduced during the movements,and removing said door from the box sufficiently rapidly that theparticulate material falls substantially as a unit into the cavity.

In a method according to the invention, the to and fro horizontal motioncauses the particulate material to form a substantially level pile inthe box, i.e. one of constant depth, and this pile is found to fallsubstantially intact into the cavity. The relatively large quantity ofenergy applied to the material in the initial movements of the to andfro movement causes larger particles in the material to be distributedacross the box while the relatively smaller quantity of energy appliedin the later movements does not significantly move said larger particlesbut distributes any smaller particles. By reducing the energyprogressively, the correct amount of energy to distribute each particlesize present, is applied at some time during the movements and oncedistributed said particles are not significantly moved thereafter. Theto and fro motion can be performed in the confined space between theplatens of a press, and the method can be used to deposit successivelayers, each of uniform depth, on top of one another. Furthermore, theto and fro motion is found to achieve a uniform distribution ofparticles of different types within a charge or layer which is presentin the material in the cavity, unlike some known charging methods whichcreate local concentrations of particles of one type. The progressivereduction in energy can be achieved by decreasing the amplitude of theto and fro movements. Alternatively, or additionally, the duration ofthe movements may be increased.

At least some of the to and fro movements may be separated by pauses,thereby giving the material more settling time before it is moved again.The pauses may last up to one quarter of the duration of the movementpreceding it.

The door, or several doors arranged to be moved simultaneously, have toclose the entire bottom of the box and be removed sufficiently rapidlythat substantially none of the material can fall before the rest. Aremoval time of about 0.2 seconds has been found to be suitable. Thedoor or doors may be removed by horizontal movement.

The to and fro movements of the box are preferably linear but mayalternatively be arcuate, circular or ellipsoidal. In some cases, it maybe advantageous to superimpose simultaneous or successive linear to andfro movements at right angles to one another, the frequencies andamplitudes of the two movements may be the same or different. Where thecavity is elongated, the to and fro movement may be parallel to themajor axis of the cavity.

There may be 5 to 10 to and fro movements, each having a durationbetween 1 second and 0.1 seconds. The exact number of movements and thedurations thereof, as well as the energy imparted, e.g. by variation ofduration or amplitude or both, are selected to suit the particularmaterial.

Provided that the box is not moved too violently to position it, it isfound that the to and fro movements can be made before the box ispositioned over the cavity which may be advantageous in somecircumstances. Alternatively, where the to and fro movements are linear,the positioning movement may be linear at right angles to the to and fromovements or in the same direction as the to and fro movement.

The particulate material may be guided from the box to the cavity, e.g.by a guide having the same horizontal cross-sectional shape as thecavity, or by an air curtain, or by a combination of such a guide and anair curtain.

Where two layers of particulate material of different types, e.g. ofdifferent compositions, mixes or particle sizes, are required, themethod may also comprise positioning a predetermined quantity of afurther particulate material in a further box mounted directly above thefirst-mentioned box, said further box also having substantially the samehorizontal cross-sectional shape as the cavity, the further box beingclosed at the bottom by at least one further door on which the furtherparticulate material rests, moving the further box to and fro with thefirst-mentioned box, and removing said further door from said furtherbox, after the first-mentioned particulate material has fallen into thecavity, the further door being removed sufficiently rapidly that thefurther particulate material falls substantially as a unit through thefirst-mentioned box into the cavity on top of the first-mentionedparticulate material.

The invention also provides apparatus for use in charging a cavity withparticulate material, the apparatus comprising a box arranged to receivea predetermined quantity of particulate material, the box havingsubstantially the same horizontal cross-sectional shape as the cavity,at least one door movable between a closed position thereof, in which itcloses the bottom of said box and particulate material in the box restson the door, and an open position thereof, in which it allowsparticulate material to fall out through the bottom of the box, boxmoving means operable to move the box and the door in its closedposition to and fro horizontally a plurality of times with movementsarranged so that the energy imparted to material in the box as a resultof the movements is progressively reduced during the movements, and doormoving means operable to move the door from its closed to its openposition sufficiently rapidly that particulate material in the box fallsthrough the bottom thereof substantially as a unit.

The box moving means may be operable to move the box to and fro along alinear track, e.g. defined by rollers.

The door moving means may be operable to move the door along ahorizontal track.

The apparatus may also comprise guidance means acting to guide theparticulate material from the box to the cavity. The guidance means maycomprise a plurality of downwardly-directed orifices arranged around thepath taken by the particulate material, and means for directing airthrough said orifices to create an air curtain around said path. Theguidance means may also comprise, additionally or alternatively, avertically-extending guide having the same horizontal cross-sectionalshape as the cavity and the box.

The apparatus preferably comprises a hopper acting to guide particulatematerial into said box. The apparatus may also comprise catching meansacting to catch any of the particulate material which escapes from thecharge as it falls from the box. Extraction means may also be providedto remove material from the catching means.

The apparatus may also comprise further box moving means operable tomove the box and the door in its closed position in a similar manner tothe first-mentioned box moving means, ie to and fro horizontally, aplurality of times with movements arranged so that energy imparted tomaterial in the box is progressively reduced, but at right angles to themovement caused by the first-mentioned box moving means. Thus, thematerial can be distributed both away and across the box.

The apparatus may also comprise a further box fixedly mounted relativeto the first-mentioned box and directly above it, the further box alsohaving substantially the same horizontal cross-sectional shape as thecavity and being arranged to receive a predetermined quantity of secondparticulate material, at least one further door movable similarly to thefirst-mentioned door but in relation to the further box, and furtherdoor moving means operable to move the further door from its closed toits open position sufficiently rapidly that particulate material fallsthrough the bottom of the further box substantially as a unit.

The apparatus may also comprise positioning means operable to positionthe box at a particulate material receiving station and subsequentlyabove a cavity. The box moving means may operate during the operation ofthe positioning means.

The invention may be utilised with particulate material made up ofplastics, metal or other materials, including material containingelongated particles. Once in the cavity, the particles may be subjectedto heat and/or pressure to form them into an article or a preform forfurther treatment.

There now follows a detailed description, to be read with reference tothe accompanying drawings, of an apparatus; which is illustrative of theinvention in its apparatus aspects, and of its method of operation whichis illustrative of the invention in its method aspects.

In the drawings:

FIG. 1 is a side elevational view of a carrying assembly of theillustrative apparatus;

FIG. 2 is a plan view of the assembly shown in FIG. 1;

FIG. 3 is an elevational view, on a slightly smaller scale, taken in thedirection of the arrow III in FIG. 1;

FIG. 4 is a vertical cross-section taken through an assembly of boxes ofthe illustrative apparatus for mounting on the carrying assembly shownin FIGS. 1 to 3;

FIG. 5 is a vertical cross-section taken through the assembly shown inFIG. 4 but taken at right angles to the direction of view of FIG. 4;

FIG. 6 is a diagrammatic side elevational view of the illustrativeapparatus, showing the assembly of boxes mounted on the carryingassembly in two positions; and

FIG. 7 is a diagrammatic plan view of the illustrative apparatus shownin FIG. 6.

The illustrative apparatus 2 (shown in FIGS. 6 and 7) is for use incharging a cavity (not shown) with particulate material. In this case,the cavity has a rectangular horizontal cross-section. The apparatus 2comprises a carrying assembly 10 shown in FIGS. 1 to 3 and an assemblyof boxes 100 shown in FIGS. 4 and 5 which are mounted on the carryingassembly 10 in a manner to be described.

The carrying assembly 10 comprises a vertically-extending mounting plate12 on which the remainder of the assembly 10 is mounted. The plate 12 isprovided with vertically elongated holes 14 (FIG. 3) through whichclamping screws (not shown) can be passed to clamp a first surface 16 ofthe plate 12 against a carriage 17 which can be moved linearly. Movingthe carriage 17 moves the assembly 10 between a first particulatematerial receiving station 4, a second particulate material receivingstation 6, and a particulate material delivering station 8 above thecavity.

The assembly 10 also comprises a bracket 18 clamped to the surface 16 ofthe plate 12. The bracket 18 carries a motor mounting plate 20 on whichan electric motor 22 is mounted. The motor 22 is a brushless servo-motorwhich has a resolver or an encoder (not shown) associated therewith toprovide feedback of the angular position of the output shaft 24 of themotor 22. The output shaft 24 (FIG. 2) projects through a hole in theplate 20 and has an arm 26 fixedly mounted thereon so that operation ofthe motor 22 causes the arm 26 to turn about the axis of the outputshaft 24. A programmable control system (not shown) is associated withthe motor 22 to control it to make predetermined turns of the outputshaft 24.

The opposite surface 28 of the mounting plate 12 to the surface 16thereof carries four rollers 30, each on a mounting 31 clamped to theplate 12. Each roller 30 can turn about a horizontal axis thereof. Therollers 30 are arranged with two at the same upper level and two at thesame lower level and define a horizontal linear track. The surface 28defines a horizontally-extending clearance groove 32 which is mid-waybetween the upper rollers 30 and the lower rollers 30. Ahorizontally-extending slot 34 passes through the plate 12 within thegroove 32.

The assembly 10 also comprises a support 40 which is mounted on the fourrollers 30 for reciprocating movement along the track defined by therollers 30 by the action of the motor 22. The support 40 comprises avertically-extending back plate 42 which has a rear surface 44 facingthe surface 28 of the mounting plate 12. Mounted on the rear surface 44are a lower and an upper horizontally-extending bracket 46. Each bracket46 carries a horizontally-extending rail 48. The upper rail 48 is abovethe upper rollers 30 and has a lower surface which is V-shaped and isreceived in corresponding V-shaped grooves in the two upper rollers 30.The lower rail 48 is below the lower rollers 30 and has an upper surfacewhich is V-shaped and is received in corresponding V-shaped grooves inthe two lower rollers 30. The upper rail 48 supports the support 40 andthe lower rail 48 guides the support 40 during reciprocating horizontalmotion parallel to the surface 28 along the track defined by the rollers30. The surface 44 also carries a boss 50 which is mid-way between thetwo brackets 46. The boss 50 has a pin 52 secured thereto which projectshorizontally into the clearance slot 34 in the mounting plate 12 (FIG.1). The pin 52 carries a ball joint 54.

In order to enable the motor 22 to move the support 40, the ball joint54 is connected by a link 55 to a ball joint 56 (FIG. 2) carried by apin 58 which projects horizontally from the arm 26 on the output shaft24 of the motor 22. The pin 58 is spaced from the output shaft 24 sothat operation of the motor 22 causes the link 55 to move the support40. The link 55 extends along the clearance groove 32 in the plate 12and is adjustable in length by a left and right-handed screw threadarrangement.

At its lower edge, the back plate 42, on its surface 44, carries anextractor pipe 60 provided with a connecting flange 62. The pipe 60extends horizontally from a hole 64 through the plate 42 with which thepipe 60 connects. The plate 42 also carries a connector 66 for an airsupply. The connector 66 is close to the hole 64 and also connects witha hole (not shown) through the plate 42.

The support 40 also comprises left and right vertically-extending sideplates 68 and 70 which are formed integrally with the back plate 42which they meet at right angles. The side plates 68 and 70 project awayfrom the plate 12. The plates 68 and 70 are generally similar to oneanother so that only the left side plate 68 need be described in detail(similar parts associated with the right side plate 70 are given thesame reference numerals).

The left side plate 68 has two horizontally-extending slitstherethrough, an upper slit 72 and a lower slit 74. The upper slits 72allow end portions of a pair of horizontally-extending upper doors 76 topass through the plates 68 and 70, each door passing through a slit inboth plates. The doors 76 are provided by thin metal sheets with anon-stick coating on their upper surfaces and extend across the spacebetween the side plates 68 and 70. The lower slits 74 allow end portionsof a lower pair of doors 78 similar to the doors 76 to pass through theplates 68 and 70. The doors 76 and 78 are slidable along horizontaltracks defined by rails 80 mounted adjacent to the slits 72 and 74 onthe inside surfaces of the plates 68 and 70. The doors 76 and 78 canslide horizontally between a closed position, in which each door engagesthe other door of the pair along an edge thereof, and an open position,in which these doors are separated. In FIG. 1, the doors 76 and 78 areshown in their closed positions and, in FIG. 2, the doors 76 are shownclose to their closed positions.

In order to move the doors 76 and 78 between their open and closedpositions, the support 40 comprises eight pneumatic piston and cylinderassemblies 82. The assemblies 82 are mounted on the outside surfaces ofthe plates 68 and 70 with each assembly 82 acting on one end of one ofthe doors 76 and 78. Each assembly 82 extends horizontally and has apiston rod 84 carrying a crosshead 85 which is fixed to a bracket 86which is also fixed to one of the doors 76 and 78. Each assembly 82carries a rubber cushion 88 arranged to cushion the impact when thedoors 76 and 78 are moved to their closed positions. The assemblies 82provide door opening means operable to move the doors 76 and 78 fromtheir closed to their open positions and back again.

The doors 76 and 78 are operated by supplying air under pressure to theassemblies 82. The assemblies 82 associated with the doors 76 areoperated together as are the assemblies associated with the doors 78 butthe doors 76 can be operated independently of the doors 78 and viceversa. The assemblies 82 are arranged so that extending the piston rods84 moves the doors to their open positions whereas retracting them movesthe doors to their closed positions at which point the crossheads 85engage the cushions 88. The assemblies 82 are arranged to move the doors76 or 78 from their closed positions to their open positions in about0.2 seconds.

The lowermost edges of the side plates 68 and 70 are turned inwards toprovide shelves (not shown) and the vertical edges away from the backplate 42 are turned outwardly to provide flanges 90 which supportthreaded fixing points 92. The side plates 68 and 70 are also connectedby two beams 94 and 96 which are disposed closer to the back plate 42than to the flanges 90.

The support 40 is arranged to support three units of the box assembly100 which are not shown in FIGS. 1 to 3 but are illustrated in FIGS. 4and 5. The assembly 100 is one of a number of alternative assemblieswhich can be mounted on the support 40, the assemblies differing in thecross-sectional shape of a central vertical passage 102 therethroughwhose shape is determined by the shape of the cavity.

The assembly 100 comprises a lower unit 104, a centre unit 106 and anupper unit 108. The units 104, 106 and 108 are constructed of sheetmaterial and are disposed one above the other on the support 40.

The lower unit 104 comprises a horizontal base plate 110 on top of whichan open-topped box is formed by vertical front and back plates 112 andtwo vertical side plates 113 so that the plate 110 forms a bottom of thebox. The base plate 110 has a central hole therethrough in which astepped block 114 is received. This block 114 defines a rectangularvertical passage in which a box 116 is mounted. The box 116 is open atthe top and the bottom and is formed of four vertically-extendingplates. The box 116 forms a lower part of the passage 102 and has ahorizontal cross-sectional shape and size which are identical to thoseof the cavity. The box 116 forms part of guidance means of the apparatusacting to guide particulate material into the cavity. A further block118 is mounted on top of the block 114 and extends around the box 116.The block 118 is cut-away to provide a small plenum chamber 120extending around the box 116 and enclosed by the blocks 114 and 118, andby a portion of the outer surface of the box 116. The plenum chamber 120has an entrance 122 through the block 118. The entrance is connected bypipes (not shown) to a connector (not shown) which plugs into theconnector 66 mounted on the support 40 so that air can be supplied tothe plenum chamber 120. The plenum chamber 120 has a large number ofexits formed by narrow vertical bores 124 in the block 114. These bores124 have exits spaced around the lower entrance of the passage 102 whichis formed by the lower periphery of the plates forming the box 116. Whenthe plenum chamber 120 is supplied with air, air passes out of the bores124 and forms a curtain of air (indicated by the arrows A) which extendsdownwardly from the passage 102. The air curtain co-operates with thebox 116 in forming guidance means to guide particulate material. Theexits of the bores 124 provide a plurality of downwardly-directedorifices arranged around the path taken by the particulate material, andthe plenum chamber 120 provides means for directing air through saidorifices to create the air curtain A around said path.

The unit 104 also comprises inclined plates 126 which are mounted withinthe box formed by the plates 112 and 113 and around the box 116. Theplates 126 have their upper ends abutting the box 116 above the block118 and their lower ends are at the junctions of the base plate 110 andthe plates 112. The inclined plates 126 direct particulate materialwhich escapes from the passage 102 into gutters formed by the junctionof the inclined plates 126 and the front and back plates 112. The gutterformed adjacent the back plate 112 is connected by a plug (not shown) tothe hole 64 into the extractor pipe 60 when the unit 104 is on thesupport 40. The other gutter is connected by a hole 128 to the interiorof an extractor pipe 130. The pipe 130, which is provided with aconnecting flange 132, extends horizontally along the outside surface ofthe front plate 112. The plates 112, 113 and 126, thus, form catchingmeans of the apparatus acting to catch any particulate material whichescapes as it passes through the assembly 100. The pipes 60 and 130provide extraction means to remove material from the catching means.

The unit 104 is mounted on the support 40 by being slid horizontallybetween the side plates 68 and 70 so that it rests on the shelves formedby the upturned lower edges of the plates 68 and 70. The upper peripheryof the box 116 is then just below the lower doors 78. Mounting the unit104 on the support 40 connects the air supply to the plenum chamber 120and the extraction pipe 60 to the rear gutter.

The centre unit 106 is mounted between the lower doors 78 and the upperdoors 76 by means of a vertical front plate 134 which engages both theflanges 90 and is bolted thereto through holes 136, the bolts enteringfour of the threaded fixing points 92. The unit 106 clears the beam 96.The plate 134 has a downward projection 138 which acts to retain thelower unit 104 on the support 40. The unit 106 also comprises a box 140which is made from four generally vertically-extending plates. The box140 has an open bottom which is the same shape and size as the open topof the box 116 of the lower unit 104 with which it is aligned so thatthe box 140 defines a central section of the passage 102. The box 140tapers inwardly, slightly, towards its top which is also open. The box140 is supported by struts 142 mounted on the front plate 134.

The box 140 is arranged to receive a predetermined quantity ofparticulate material, through its open top, when the doors 76 are intheir open positions. The box 140 has substantially the same horizontalcross-sectional shape as the cavity and as the box 116. When in theirclosed positions, the lower doors 78 close the bottom of the box 116 sothat particulate material in the box 140 rests on the doors 78.

The upper unit 108 is mounted on the support 40 above the upper doors 76by means of a vertical front plate 144 which engages both flanges 90 andis bolted thereto by bolts entering four of the fixing points 92 throughholes 146. The unit 108 clears the beam 94. The unit 108 also comprisesa box 150 and a hopper 152 mounted above the box 150. The box 150 andthe hopper 152 are made from four plates each supported by the frontplate 144 by means of struts 154. The plates forming the box 150 arevertical and the box has an open bottom which is just above the doors 76and is the same shape as the open top of the box 140 of the centre unit106. The box 150 forms an upper section of the passage 102. The top ofthe box 150 is open and communicates with the bottom of the hopper 152.The plates of the hopper 152 incline outwardly in the upwards directionso that the open top of the hopper is larger than its open bottom.

The box 150 provides a further box of the apparatus fixedly mounted onthe support 40 relative to the box 140 and directly above it. The box150 has substantially the same horizontal cross-sectional shape as thecavity and is arranged to receive, through its open top, a predeterminedquantity of a second particulate material which rests on the doors 76when they are in their closed positions in which they close the bottomof the box 150. The doors 76 and their associated assemblies 82 act inthe same way in relation to the box 150 as do the doors 78 and theirassociated assemblies 82 in relation to the box 140.

The hopper 152 acts to guide particulate material dropped into its upperend into the box 150. The hopper 152 guides not only a secondparticulate material which is destined for the box 150, but also a firstparticulate material which is destined for the box 140, this materialpassing through the box 150 to reach the box 140.

The apparatus 2 also comprises a further servo-motor 160 (FIG. 7) whichprovides both positioning means operable to position the boxes 140 and150 at the stations 4, 6 and 8 and also a further box moving meansoperable to move the boxes 140 and 150 in the same way as the motor 22but at right angles to the movement caused by the motor 22.

The motor 160 is mounted on a framework 162 of the apparatus 2 whichalso supports two horizontal rails 164 (only one visible in thedrawings). The rails 164 extend from the receiving station 4 to thereceiving station 6 and from there to the delivery station 8 at whichthere is a press 166. The carriage 17 runs on the rails 164 so that theboxes 140 and 150 can be positioned at the stations 4, 6 and 8 (althoughthe apparatus 2 has only one carriage 17, it is shown in FIGS. 6 and 7at both the stations 4 and 8). The framework 162 also supports a ballscrew 168 by which the carriage 17 is driven along the rails 164. Theball screw 168 is operated by the motor 160.

In the operation of the illustrative apparatus 2 by the illustrativemethod, a predetermined quantity of a first particulate material ispositioned in the box 140 and a predetermined quantity of a secondparticulate material is positioned in the box 150. This is achieved byoperating the motor 160 to move the assembly 100 to the first receivingstation 4, where it is beneath a weigh cell operable to weigh apredetermined quantity of the first particulate material. Then, with theupper doors 76 open and the lower doors 78 closed, the weighed materialis dropped into the top of the hopper 152. The first particulatematerial is guided by the hopper 152 into the box 150 and falls downinto the box 140 where it rests on the doors 78. The assembly 100 isthen moved by operation of the motor 160 to the second receiving station6, where it is beneath a second weigh cell and the piston and cylinderassemblies 82 are operated to close the upper doors 76. The second weighcell is operable to weigh a predetermined quantity of the secondparticulate material. The weighed quantity of the second material isdropped into the top of the hopper 152 and is guided into the box 140where it rests on top of the upper doors 76.

The assembly 100 is now moved to the delivering station 8 between theplatens of the press 166 above the cavity, and the motors 22 and 160 areoperated to level the particulate material. The motor 22 provides boxmoving means of the apparatus operable to move the boxes 140 and 150 andtheir doors 78 and 76 (in the closed positions) to and fro horizontallyalong the linear horizontal track defined by the rollers 30. This isachieved by turning the output shaft 24 through an arc of 180° or lessso that the arm 26 turns and moves the link 55 along the groove 32. Themovement of the link 55 causes the support 40 and all parts mountedthereon to move relative to the mounting plate 12 with the rails 48running on the rollers 30. The to and fro movements are arranged so thatthe energy imparted to the material in the boxes 140 and 150, as aresult of the movements, is progressively reduced during the movements.This is achieved by the signals of the control system to the motor 22causing each successive arcuate turn of the output shaft 24 to bethrough a smaller angle. The amplitude of the to and fro movements ofthe boxes 140 and 150 is, thus, progressively reduced. The firstmovement may be caused by a 180° turn of the motor, the second by a 162°turn in the opposite direction, the third by a 149° turn in the firstdirection, and so on. Eight to and fro movements are made, i.e. sixteenmovements in total, which are of progressively decreasing amplitude. Inthe first movement, the particulate materials have a relatively largeamount of energy imparted thereto and in each subsequent movement theenergy imparted is less. These to and fro movements are found to producea level pile of particulate material in each of the boxes 140 and 150and, where there are different types of particle in the material, thesetypes are found to be well-distributed in the piles.

If the shape of the cavity is such that the levelling movements impartedby the motor 22 are insufficient, further levelling movements can beapplied (at right angles) by operating the motor 160 to oscillate thecarriage 17 along the rails 164 with an energy decreasing oscillation.

If the passage 102 is not exactly aligned with the cavity after the toand fro movements, the boxes 140 and 150 are moved into this position bygentle movements of the assembly 10. The air supply to the plenumchamber 120 is now turned on creating a curtain of air extendingdownwardly from the box 116 to the mould cavity. The assemblies 82 arenow operated to open the lower doors 78. The doors 78 are, thus, removedfrom the box 140 sufficiently rapidly that the first particulatematerial falls substantially as a unit into the cavity. The doors 78 aremoved horizontally along the rails 80. The first particulate materialfalls through the box 116 into the mould cavity being guided by the box116 and the air curtain. Next, the assemblies 82 are operated to rapidlyopen the upper doors 76. Like the doors 78, the doors 76 and removedsufficiently rapidly that the second particulate material falls out ofthe bottom of the box, in this case the box 150, substantially as aunit. The second particulate material falls through the boxes 140 and116 into the mould cavity being also guided by the box 116 and by theair curtain. The second particulate material lands on top of the firstparticulate material. The material is found to arrive in the mouldcavity substantially in the same level state and distribution in whichit was in the boxes 140 and 150. Any particulate material which escapesinto the gaps between the boxes 140 and 150, and the boxes 140 and 116falls into the gutters and is extracted through the pipes 60 and 130.

We claim:
 1. A method of charging a cavity with particulate material,the method comprising positioning a predetermined quantity ofparticulate material in a box which has substantially the samehorizontal cross-sectional shape as the cavity, the box having an openbottom closed by at least one door on which the particulate materialrests, moving the box containing the particulate material to and frohorizontally with respect to said cavity a plurality of times withmovements arranged so that the energy imparted to the material as aresult of the movements is progressively reduced during the movements,and removing said door from said open bottom of said box sufficientlyrapidly that the predetermined quantity of particulate material fallssubstantially as a unit into the cavity.
 2. A method according to claim1, characterised in that the energy is reduced by decreasing theamplitude of the to and fro movements.
 3. A method according to claim 1,characterised in that the energy is reduced by increasing the durationof the to and fro movements.
 4. A method according to claim 1,characterised in that at least some of the to and fro movements areseparated by pauses.
 5. A method according to claim 1, characterised inthat the door is removed by a horizontal movement thereof.
 6. A methodaccording to claim 1, characterised in that the to and from movements ofthe box are linear.
 7. A method according to claim 1, characterised inthat the to and fro movement are made before the box is positioned overthe cavity.
 8. A method according to claim 1, characterised in that theparticulate material is guided from the box to the cavity.
 9. A methodaccording to claim 1, characterised in that the method also comprisespositioning a predetermined quantity of a further particulate materialin a further box mounted directly above the first-mentioned box, saidfurther box also having substantially the same horizontalcross-sectional shape as the cavity, the further box being closed at thebottom by at least one further door on which the further particulatematerial rests, moving the further box to and fro with thefirst-mentioned box, and removing said further door from said furtherbox, after the first-mentioned particulate material has fallen into thecavity, the further door being removed sufficiently rapidly that thefurther particulate material falls substantially as a unit through thefirst-mentioned box into the cavity on top of the first-mentionedparticulate material.
 10. Apparatus for use in charging a cavity withparticulate material, the apparatus comprising a box arranged to receivea predetermined quantity of particulate material, the box havingsubstantially the same horizontal cross-sectional shape as the cavity,at least one door movable between a closed position thereof, in which itcloses the bottom of said box and particulate material in the box restson the door, and an open position thereof, in which it allowsparticulate material to fall out through the bottom of the box, boxmoving means operable to move the box and the door in its closedposition to and fro horizontally with respect to said cavity a pluralityof times with movements arranged so that the energy imparted to materialin the box as a result of the movements is progressively reduced duringthe movements, and door moving means operable to move the door from itsclosed to its open position sufficiently rapidly that said predeterminedquantity of particulate material in the box falls through the bottomthereof substantially as a unit.
 11. Apparatus according to claim 10,characterised in that the box moving means is operable to move the boxto and fro along a linear track.
 12. Apparatus according to claim 10,characterised in that the door moving means is operable to move the dooralong a horizontal track.
 13. Apparatus according to claim 10,characterised in that the apparatus also comprises guidance means actingto guide the particulate material from the box to the cavity. 14.Apparatus according to claim 13, characterised in that the guidancemeans comprises a plurality of downwardly-directed orifices arrangedaround the path taken by the particulate material, and means fordirecting air through said orifices to create an air curtain around saidpath.
 15. Apparatus according to claim 10, characterised in that theapparatus also comprises a hopper acting to guide particulate materialinto said box.
 16. Apparatus according to claim 10, characterised inthat the apparatus also comprises further box moving means operable tomove the box and the door in its closed position in a similar manner tothe first-mentioned box moving means but at right angles to the movementcaused thereby.
 17. Apparatus according to claim 10, characterised inthat the apparatus also comprises a further box fixedly mounted relativeto the first-mentioned box and directly above it, the further box alsohaving substantially the same horizontal cross-sectional shape as thecavity and being arranged to receive a predetermined quantity of asecond particulate material, at least one further door movable similarlyto the first-mentioned door but in relation to the further box, andfurther door moving means operable to move the further door from itsclosed to its open position sufficiently rapidly that particulatematerial falls through the bottom of the further box substantially as aunit.
 18. Apparatus according to claim 10, characterised in that theapparatus also comprises positioning means operable to position the boxat a particulate material receiving station (4) and subsequently above acavity.